As animals move about in the environment, they must be able to rapidly assess and update the meaning of cues around them in order to approach reward and avoid danger. Reversal learning, a paradigm commonly used to test behavioral flexibility, involves switching the association between a stimulus and its outcome. For example, a tone that initially predicted a sweet tastant can come to predict a bitter tastant. Two brain regions, the orbitofrontal cortex (OFC) and basolateral amygdala (BLA), are involved in tasks that demand flexible responses to the changing significance of stimuli during reversal learning. While several studies have provided evidence that the OFC and BLA interact during reversal learning, little is known about the specific mechanisms of this interaction. In this grant, we propose to use a combination of genetic and cellular imaging techniques in mice to identify and characterize the physiological response properties during reversal learning of BLA neurons that project to OFC. The reversal learning task we employ involves stimuli of multiple modalities that predict outcomes of both positive and negative value to thoroughly elucidate the differential response properties of BLA neurons to stimuli that change their associated reinforcement outcome (Aim 1). In these experiments, the physiological response properties of neurons identified as projecting from BLA to OFC will be compared to the response properties of the overall population. Then, using an optogenetic approach, we will test the causal role of OFC input onto BLA neurons during reversal learning by inhibiting the specific projections from OFC to BLA to test their causal role on behavioral flexibility and on the nature of representations in BLA (Aim 2). The data analysis for both aims involves collaboration with theoretical neuroscientists to use linear classifiers and other sophisticated techniques to understand the nature and dynamics of neural encoding in BLA and its relation to behavior. These experiments promise to shed light on the mechanisms by which cortico-amygdalar circuits mediate flexibility critical for adaptive emotional responses and behavior, an ability that is impaired in individuals with psychiatric disorders.